Thermally insulating composite frame members for windows, curtain walls, storefront framing systems, and the like are known wherein elongated inner and outer metallic frame members are structurally interconnected by a thermal isolator formed of a plastic or other material. For example, U.S. Pat. No. 4,330,919 to Bischlipp discloses a connecting element which has two elongated profiled members bounding with one another in a channel wherein the two elongated profiled members are connected with at least two thermal separating members. The thermal separating members are formed by supplying a hardenable heat insulating material into the sections of the channel so as to harden and to form the heat insulating inserts separated from the intermediate hollow space by the bottom walls. The metallic profiled members together with the bottom walls form a unitary one-piece profiled element. In order to thermally isolate the metallic profiled members, a de-bridging operation is needed wherein a grinding tool is inserted into the intermediate hollow space for removal of selected portions of the profile material to separate the bottom walls from the remainder portions of the profiled members as well as to remove the same from the intermediate hollow space. De-bridging is a costly, dirty, and time consuming procedure.
U.S. Pat. No. 5,469,683 to McKenna discloses a thermally insulating composite frame member having a snap-in thermal isolator and which overcomes the need for a de-bridging operation wherein the snap-in thermal isolator is an elongated extrusion of generally H-shaped cross section. The complicated H-shape is necessary to hold the inner and outer frame members in alignment during assembly of the composite frame member. In this regard, the disclosed thermal isolator includes a pair of resilient, spaced apart legs projecting forward from an outwardly facing portion of the isolator. A second pair of resilient, spaced apart legs project rearward from an inwardly facing portion of the isolator. Each of the first and second pairs of spaced apart legs forms a jaw-like clamp configured to engage and to secure about a corresponding one of the facing flanges. In order to improve the shear force characteristics of the construction, the isolator of the disclosed embodiment is adhesively bonded to the gutter member and to the frame member in addition to the mechanical coupling provided by the jaw-like clamps of the isolator. Also in the disclosed embodiment mutually engaging surfaces of each of the jaw-like clamps and their respective flanges are knurled to provide further enhanced resistance to longitudinal shear forces.